McNair, 19, had looked comfortable in his previous four starts for the club and was on the winning side in all of them, gaining several plaudits along the way.
But in an unfamiliar 3-5-2 formation and amidst another change early in the game, McNair was a shadow of his previous self, making several mistakes and giving the ball away under pressure.
It forced Van Gaal into a move that didn’t make any United supporter, coaching member or probably player happy as it’s never pleasant to see a player subbed for a poor performance but the boss is adamant it was the right thing to do.
Van Gaal said: “He had no confidence, he had given three chances away.
“It’s very disappointing for me and also for Paddy but I had to because as a manager I am responsible [for the] win.
“After the change we played a little bit better. Of course it is tough but it is also in his best interests.
“I have made a lot of [early] changes and all the boys can survive. It is only one moment in their lifetime.”
It was a move United supporters probably wouldn’t have seen under David Moyes but it made a refreshing change to see a manager so pro-active and realise the key weakness in his team and rectify it early on.
Van Gaal was blunt in his assessment which may seem harsh but all he was doing was correcting the issues in the side which ultimately proved right given that United won.
McNair will have an easier time mentally recovering from being taken off early on in a game United went on to win than it would have been had McNair stayed on and contributed to a United loss.
The experienced Michael Carrick moved into the back three and performed well as United’s once again makeshift defence held out under late pressure to walk away with another valuable three points.